The morphology and growth of extended chain crystals of polyethylene is discussed on the basis of optical and electron microscopy. The spherulitic habit is shown to be caused by nucleation of new lamellae on the (001) surface of lamellae, branching of lamellae on their growth face, and thickening of lamellae. Spherulite centers have been identified down to the primary lamella. Analysis of intersections of lamellae during crystallization allowed the identification of intermediate stages of crystal growth. Fracture surfaces parallel to the growth face and the (001) face are discussed. "Ripple decoration" by surface recrystallization is developed as a tool for fracture surface study. Kink bands are described as growth defects. Bending of lamellae is shown to go by slip parallel t o the polymer chains. Ripple and drawn out fiber annealing is analyzed. .ill observations on extended chain crystals are used to propose a mechanism of extended chain crystal growth of polyethylene under elevated pressure. ZUSAMMENFASSUNG:Die Morphologie und das Wachstum von gestrecktkettigen Polyathylenkristallen werden an Hand von optischer und Elektronenmikroskopie diskutiert. Die sphirolithische Gestalt wird durch Keimbildung neuer Lamellen auf der (001)-Oberflache von Lamellen, Verzweigung von Lamellen an der Wachstumsoberflache und Dickenwachstum hervorgerufen. Der Sphirolithkern wird bis zur Primiirlamelle identifiziert. An ifberschneidungen von Lamellen wahrend der Kristallisation sind Zwischenstufen des Kristallwachstums festgestellt wordea. Uber Bruchflachen parallel zur Wachstumsoberflache und der (OOl)-Oberflache wird diskutiert. ,,Ripple decoration'' durch Oberflachenrekristallisation wird zum Studium der Bruchoberflachen verwandt. Kinkbander werden als Wachstumsdefekte beschrieben. Lamellendeformation erfolgt durch Gleiten parallel zu den Polymerketten. Das Tempern von ,,Ripples" und ausgezogenen Fasern wird untersucht. Alle Beobachtungen an gestrecktkettigen Kristallen werden benutzt, um einen Mechanismus fiir das Wachstum von gestrecktkettigem Polyathylen unter hohem Druck vorzuschlagen.

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Differential thermal analysis and electron microscopy of partially molten, extended‐chain polyethylene crystals, grown under elevated pressure, was performed. It could be shown that melting peaks on the low temperature side of the main melting peak are due to narrowly distributed, low molecular weight polymer segregated in extended‐chain crystals. Superheating of crystals before melting increased with molecular weight and chain extension. The melting mechanism of extended chain crystals was shown to be a successive peeling off of chains which leaves the chain extension constant up to melting of the last crystal trace.

Rough fracture surfaces of extended-chain polyethylene crystals become unstable at temperatures below the bulk melting point. There is no way for the extended chains, which are up to 20,000 methylene units long, to change position without collapse. As a result, the rough surfaces smooth out on heating by covering themselves with oriented folded-chain lamellae.